Following the events described in Gray Tide in the East in which Kaiser Wilhelm made the decision to cancel the scheduled invasion of Belgium and to send his armies east against Russia, Germany has emerged from the ensuing conflict as a dominant power in the world. Britain and the United States have not yet been involved in war with Germany, and the Austro-Hungarian Empire is, as yet, intact.

Tidal Effects is an alternative history, following two major scenarios occurring in 1923 after the end of the Great European War. Firstly, US Intelligence has reported the likelihood that a major naval base is being constructed by Germany in the former French colony of Martinique. This, of course, would be intolerable, being so close to the coast of the USA, and diplomacy alone seems unlikely to resolve the issue. Secondly, Emperor Charles (Karl) I of Austria is facing unrest within the Empire and, worse, the persistent involvement of Germany in his affairs. The only way forward is to form an alliance with other powers not yet under Germany's influence, but with Austria's political and diplomatic infrastructure riddled with German agents and sympathizers, any such plan would be sabotaged before it started.

He needs to find someone who can meet with the heads of state without arousing suspicion, someone sympathetic to those opposing Germany's expansionist plans, and yet someone whose high-level meetings will not alert Germany to his true mission. There is just one man who might be able to do it....